Blizzard puts out holiday cards -- actually created for employees to send to work contacts -- that feature whatever the art team wanted to show off. Since they leaked online for years, now they just show them off publicly. Sometimes they reflect what's being worked on or what's coming up, sometimes they're just what would work best for a Christmas card (lots of orcs in snowball fights, etc.).
This image might not have been originally intended as a marketing image. In which case, trying to read the tea leaves about what it mean is a probably waste of time.